Coplanar camera scanning system

ABSTRACT

A system for scanning objects having a linear array sensor, adapted to detect light input signals, is provided. A lens is optically connected to the linear array sensor, and is adapted to receive and transmit an optical image located in a field of view along a lens axis to the linear array sensor. A light source which generates an illumination stripe in general linear alignment with the lens axis is provided. A cylindrical lens is positioned between the light source and an object to be scanned. The cylindrical lens adapted to collect, transmit and focus light from the light source to form the illumination stripe.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/810,204, filed Mar. 16, 2001, which claims the benefit of U.S.Provisional Application No. 60/190,273, filed Mar. 17, 2000.

BACKGROUND

[0002] The present invention relates generally to optical scanningsystems. More particularly, this invention relates to a scanning systemcontaining a camera using a coplanar light source.

[0003] Various optical scanning systems have been developed for readingand decoding coded symbologies, identification of objects, comparison ofobjects, and measurement of objects. Each of these scanning systemsutilizes either a non-coherent or coherent light source. Lighting is oneof the key elements in obtaining good image quality. The intensity oflight needed for scanning is directly proportional to the transportspeed of the scanned object and the speed of the sensor. Generally, thefaster an image is to be acquired, the more light is needed. Until now,only high intensity sodium or halogen lighting was adequate to obtaincrisp images in cameras that focus over a significant depth of field athigh speeds. The light source is usually located off axis from thecamera and sensor detecting the light reflected from the object beingscanned.

[0004] In applications using sodium lamps as a light source, the lampsare used to provide the illumination required by the camera detectionmeans. These lamps provide an abundance of optical power because theyare very bright and have a wide spectral range. There are, however,several disadvantages to sodium lamp light sources. First, due to theirextreme brightness, sodium lamps can create an annoyance and possiblehazard to workers working in the vicinity of the scanning systems.Second, sodium lights require a large amount of AC power, thusincreasing production costs. Third, these light sources create a largeamount of heat. Additionally, radio frequency interference can becreated which can present operational problems to equipment in thevicinity of the scanning system.

[0005] The use of light sources such as LEDs presents several advantagesover sodium and halogen lighting. LED illumination is a more costeffective and ergonomic method of illumination. The problem presented byLED illumination is how to get enough light to the object that is beingimaged when focusing over a large depth of field. By eliminating themounting angle between the light source and the line of sight of thecamera lens, the reflected light is managed and a lower intensity lightsource may be used. Because LEDs can be energized almostinstantaneously, they can be de-energized when objects are not beingtransported within the field of view. This extends the life of the LEDsand also conserves power. Additionally, the power input to individualLEDs may be modulated and pinpointed to a desired area, such thatdifferent LEDs within an LED array may be energized at different levelsaccording to the desired application.

[0006] The use of a coherent or non-coherent light source which willprovide sufficient optical illumination to an object to be scanned,which uses less energy while alleviating potential problems of radiofrequency interference or heat emission is needed.

SUMMARY OF THE INVENTION

[0007] Briefly stated, the present invention provides an opticalscanning system which uses a light source to provide an illuminationstripe that is coplanar to a camera lens and light sensor for barcodereading applications. The light source may be coplanar to the lens axisand light sensor, and preferably is formed from LEDs or other low powerconsumption illumination sources. The coplanar design provides adequateillumination for a large depth of field at low speeds.

[0008] In another aspect, the invention provides a scanning system inwhich the light source is shifted relative to the line of sight of thecamera such that the illumination stripe remains coplanar with thecamera line of sight at the required depth of field. The light stripeprofile coming from the array can therefore be narrow. The intensity oflight required to illuminate an object over the depth of field issignificantly reduced, thus allowing for the use of an LED array orother low power light source.

[0009] In another aspect, the invention provides a plurality of off-axislight sources to provide an illumination stripe on the object generallycoplanar with camera line of sight at the required depth of field.Different arrays of lights sources are energized according to the depthof field of the target object, allowing adequate lighting over a rangeof distances.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a side view of the coplanar camera in accordance withthe preferred embodiment of the present invention.

[0011]FIG. 2 is a top view of the coplanar camera in accordance with thepreferred embodiment of the present invention.

[0012]FIG. 3 is a front isometric view of the coplanar camera inaccordance with the preferred embodiment of the invention.

[0013]FIG. 4 is a side isometric view of a second embodiment of theinvention with a movable array of light sources used in an off-cameralens axis orientation in accordance with the present invention.

[0014]FIG. 5 is a side isometric view of a multiple row large depth offield illuminator in accordance with the present invention.

[0015]FIG. 6 is an end view of a movable light source in accordance withthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described with reference to thedrawing figures wherein like numerals represent like elementsthroughout.

[0017] Referring to FIG. 1, a coplanar camera scanning system 10 inaccordance with the present invention is shown. The coplanar camerascanning system 10 preferably includes a light source 11, a camera lens12, a focusing ring 13 for the lens 12, a linear array sensor 14, awindow 22, a cylindrical lens 18, and a voice coil actuator 16. In thepreferred embodiment, the light source 11 is comprised of one or morevery high intensity LED arrays, although those skilled in the art willrecognize other suitable lighting could be utilized, such as lasers or alaser line generator.

[0018] The light source 11 is used to illuminate a surface of a targetobject, indicated by broken line 17. The emitted light illuminates thetarget object and is reflected back to the coplanar aligned sensor 14.The coplanar camera scanning system lo is preferably used to readbarcode information from the scanned object. The coplanar camerascanning system 10 preferably utilizes a CMOS linear array sensor 14 todetect the light reflected from the object being scanned. In the firstpreferred embodiment a CMOS-based image sensor is referenced, but asthose skilled in the art should know, any image sensor can be used,e.g., a CCD-based image sensor. The light reflected onto the CMOS lineararray sensor 14 is generated in the preferred embodiment by very highintensity LEDs 11. The preferred embodiment of the present inventionutilizes red LEDs within the array. As the technology regarding lightsources advances, brighter, more intense LEDs can be used, includingLEDs having different wavelengths. Also low power semiconductor laserscan be utilized.

[0019] The LED array 11 acts as the light source for the coplanar camerascanning system 10. As shown in FIG. 2, in the first preferredembodiment of the present invention, the light source 11 is positionedparallel to, and in the same plane as the CMOS linear array sensor 14.Those skilled in the art should realize that the light source 11positioned in this manner is on-axis with the CMOS linear array sensor14. The light source 11 preferably comprises a plurality of LEDs inseries with each other, located on one or more circuit boards 31. Inthis embodiment, the coplanar camera utilizes two LED arrays to generatethe required amount of light. In this embodiment, the light source 11 ispositioned on each side of the camera lens 12. As should be clear tothose skilled in the art, the number of LEDs required for each lightsource 11 differs based on the size of the conveyor belt and requireddepth of field. The present invention preferably utilizes 50 LEDs ineach of the up to four arrays, totaling 200 LEDs. Alternatively, adesired number of low power semiconductor laser arrays may be mounted onthe circuit board 31.

[0020] The light emitted from the light source 11 is focused to a narrow“stripe” on the object using a cylindrical lens 18. This cylindricallens 18 is positioned parallel to and in between the light source 11 andthe target object. In the present preferred embodiment a Fresnel lens isused, but as those skilled in the art should realize, any optical lenscan be used in this application. As shown in FIGS. 1 and 2, thepositioning of the cylindrical lens in relation to the light source 11provides a narrow “stripe” of light anywhere within the depth of field.When the target object enters this scanning field, the illumination fromthe light source 11 illuminates the object. Due to the positioning ofthe sensor 14 relative to the light source 11, the CMOS linear arraysensor 14 detects the most intense light provided by the light source11.

[0021] As shown in FIGS. 1 and 3, the cylindrical lens 18 includes acenter slit 20.

[0022] This center slit 20 permits the light reflected from the targetobject to return through the cylindrical lens 18 to the camera lens 12and then projected onto the CMOS linear array sensor 14.

[0023] In order to maximize the depth of field of the coplanar camerascanning system 10, the voice coil actuator 16 is coupled to thefocusing ring 13 of the imaging lens 12 to dynamically focus the imageonto the CMOS linear array sensor 14, based on a signal from a rangefinder 24. Those skilled in the art should recognize that there are manymethods and apparatuses that can be used as range finders and forfocusing. The signal received from the range finder 24 causes the voicecoil actuator 16 to move the camera lens 12 and focus the lightreflected from the object onto the linear array sensor 14.

[0024] Optionally, the invention may include a focusing mechanism 26 forthe light source to more accurately focus the emitted light onto ascanned object. This enhances the image which is received by the cameralens 12 and projected onto the CMOS linear array sensor 14. The focusingmechanism 26 is coupled to the light source 11, and dynamically movesthe position of the lens 18 with respect to the position of the lightsource 11. It should be noted that either the focusing mechanism 26 orthe light source 11, or both, may be moved to focus the light. Suchmovement, of course, depends on the distance of the object from theco-planer camera 10. This alternative embodiment keeps the intensity ofthe illumination stripe maximized at any distance, providing a cleanerimage for detection by the CMOS linear array sensor 14.

[0025] Referring to FIG. 4, a second embodiment of the present inventionuses an off axis light source 40 which is located off the camera lensaxis and the linear array sensor, as represented by lines 43. The offaxis light source 40 illuminates a target object by directing a beam oflight onto its surface. However, the focused illumination stripe 44 iscoplanar with the camera lens axis 43 and the linear sensor array at therequired depth of field. The off axis light source 40 is preferably amovable array of LED sources 45 adapted to provide light to the targetobject. The invention, however, is not limited to this particularconfiguration or light source, as those skilled in the art willrecognize alternative light sources from those described, such assemiconductor lasers, may be used.

[0026] The light source 40 may be focused by using an optional lens 41.The lens 41 may be any optical type lens, although a Fresnel lens ispreferred. A light source positioner 42, preferably in the form of acontrollable motor is connected to the light source 40 to allow movementof the light source 40. The positioner 42 is adapted to move the lightsource 40 based on a height of an object to be scanned, such that thefocused illumination stripe 44, 44′ is located on the surface of theobject. The object height may be determined by a range finder or othermeans.

[0027] As shown schematically in FIG. 5, the position of the off axislight source 40 is infinitely variable. Accordingly, the illuminationstripe 44, 44′, 44″ can be shifted to multiple positions depending onthe required depth of field along the axis 43.

[0028] Referring to FIG. 6, a third embodiment of the invention is shownwhich includes multiple arrays of light sources 51 which are located onone or more circuit boards 52 placed off-axis to the lens 53 and thelinear array sensor. A range finder 50 is connected to the array oflight sources 51. The range finder 50 determines distance between thecamera and the target object. The distance data is sent to a controllerwhich then powers on or off selected arrays of light sources 51 focusedto a corresponding depth of field 55, 55′, 55″, 55′″ providing anillumination stripe 56, 56′, 56″, 56′″ coplanar to the camera lens axis57. The camera 53 and lens 54 detect the reflected light from theillumination stripe to read required data from the object.Alternatively, all of the light sources 51 may be activated to providethe desired illumination stripe at any depth of field, eliminating theneed for the distance to the target object

[0029] While the preferred embodiment of the invention has beendescribed in detail, the invention is not limited to the specificembodiment described above, which should be considered exemplary.Further, modifications and extensions of the present invention may bedeveloped based upon the foregoing, all such modifications are deemed tobe within the scope of the present invention.

What is claimed is:
 1. A system for scanning objects comprising: alinear array sensor, adapted to detect light input signals; a lensoptically connected to the linear array sensor, the lens adapted toreceive and transmit an optical image located in a field of view along alens axis to the linear array sensor; a light source which generates anillumination stripe in general linear alignment with the lens axis; anda cylindrical lens positioned between the light source and an object tobe scanned, the cylindrical lens adapted to collect, transmit and focuslight from the light source to form the illumination stripe.
 2. Thesystem for scanning objects of claim 1, further comprising: a focusingdevice connected to the lens; an actuator connected to the focusingdevice; and a range finder connected to the actuator, the range finderadapted to determine a target object distance from the lens and togenerate and transmit target object positioning data to the actuator. 3.The system for scanning objects of claim 1, further comprising: a lightsource focusing mechanism connected to the cylindrical lens, thefocusing mechanism adapted to move the cylindrical lens to focus theillumination stripe at a desired depth of field along the axis.
 4. Thesystem of claim 1, wherein the light source includes multiple linearrows of light emitters.
 5. The system for scanning objects of claim 4,further comprising: a controller connected to the light source, thecontroller adapted to energize and de-energize selected linear rows ofthe light emitters.
 6. The system for scanning objects of claim 1,wherein the cylindrical lens is a Fresnel lens.
 7. The system forscanning objects of claim 1, wherein the linear array sensor is a CCDimage sensor.
 8. The system for scanning objects of claim 1, wherein thecylindrical lens has a center slit.
 9. The system for scanning objectsof claim 1, wherein the light source is an LED array.
 10. The system forscanning objects of claim 9, wherein the LED array comprises very highintensity red LEDs.
 11. The system for scanning objects of claim 1,wherein the light source is a semiconductor laser array.
 12. The systemof claim 1, wherein the light source is coplanar with the linear sensorarray and the lens axis.
 13. The system for scanning objects of claiml,wherein the light source is moveable, and is located parallel to thelinear sensor array in a position offset from the lens axis.